Hoegel has admitted to injecting patients with drugs that cause heart failure or circulatory collapse so he could then try to revive them and, when successful, shine as a saviour in front of his colleagues.

He was found guilty of six killings in two earlier trials, but investigators have pushed on with toxicology tests on hundreds more exhumed bodies.

On Monday, Oldenburg prosecutors said they had charged him with 97 additional murders on top of the six he has been convicted of, while saying toxicology tests did not find conclusive proof in three more cases.